Method of producing and maintaining vacuums.



W. D. COOLIDGE.

METHOD OF PRODUCING AND MAINTAINING VACUUMS.

APPLICATION 'FILED FEB-5.1916.

1,289,672. Patented De0.31,1918.

Fig. l.

Inventor William D.Co olidge,

HIS fitc.

orne g.

' are subjected to electron bombardment gas PATENT OFEIcE.

WILLIAISI n. COOLIDGE, OF SCHENEGTADY, NEW YORK, ASSIGNOR T0 GENERAL Ec'rErc oomrm, A CORPORATION OF NEW YORK.

METHOD 0 rnODUcINe ANDMAINTA'INING vacuums.

Dec. 31, 1918.-

Specification of Letters Patent.

Patented Application filed February- 5', 1916. a Serial No. 76,349.

To an whom it may concern:

Be it known that I, WILLIAM D. CooLmeE, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and usefulImprovements inMethods of Producing and Maintaining Vacuums, of which the following'is a specification.

The present invention relates to the auto-,

matic maintenance of a desired-high vacuum inan electric apparatus operating with an electron discharge, such :for example, as an X-ray tube, to ionization of gas. Y

- In a device oiperating with a substantially pure electron ischarge, such, for example, as the X-ray tube described in the Physical Review for December, .1913, it is necessary to .maintain .the pressure of residual gas below a low limitin value in 'order that positive ionization will be negligible. The complete removal of gas. from the space within the envelop alone is not sufiicient to insure freedom from gas ionization during the operation'of the device, for as soonas the anode and other parts .of the apparatus is evolved. In some casessubstantially all disengageable gas is removed during the harm is one;

evacuatln 'process from parts of the apparatus sub ect to electron bombardment but the com lete removal of gas ismot always practica le. I

In accordance .with my invention the requisite vacuum is maintained during the device by automatically disinte'gr electrically a metal w thin the container in response to incipient ositive ionization of evolved as, therebyingthe gas before My inventionin one of its aspects includes a cathode of novel construction comprising an incandescent filament and 'soft metal whichis easily sputtered electrically. I In the accompanying drawing I have shown an. X-ray device as illustratlve of one form of apparatus to which my mventlon 1s applicable. Figure 1 is a somewhat diagrammatic pers ective view of an X-raytube; Figs. 2 an .3 are-enlarged detail views. taken at right anglesto each other of-a; form Of'cat ode construct-ion, and- Fig. 4' is a diagram showing an X-ray tube supplied with direct current. 1

prevent harmful positive Figs. 2 and 3, comprises a spiral filament 4 consisting preferably oftungsten, and a surrounding tube 5 consisting'of a refractory metal such as molybdenum. Electrical connections are made to the cathode filament by a tungsten Wire 6c'onnected directly to the spiral, and a tungsten wire 7 connected to" the ring 5 which is in turn welded to the opposite end of the'cathode spiral 4, as indicated at 8. The wires 6 and 7 are sealed-into a glass stem 9. Connected to the-tube a flange 10 extending at right angles to-the tube 5, and consisting preferably also of molybdenum or other highly refractory metaL- To the outer periphery of the flange 10 in "some cases is riveted, or otherwise fastened, a' ring 11 of copper, silver, gold, or other metal which may be readily sput- Referring to glass envelop 1 in which areop-' tered electrically by positive ion bombarda.

ment. It is thezfunction of the tube .5 to so i modify the electrostatic field about the oath-5' ode as to concentrate'the cathode rays upon a small spot on the anode. The rings 10 and 11 intercept positive ions which are attracted to the negative terminal of the-dv1ce.

more fully explained. The anode of the 13 of tungsten. The tube 12 is fastenedinto a tube 14 Of iron which is in turn sealed intothe arm 15 of the X-ray bulb; the glass ring The impact of positiye ionsorthe flange 11 sputters or vaporlzes metal and improves the vacuum, as will be hereinafter 16 serves to center and support the iron tube. A cooling fluid, such as watef,.- may be introduced through a supply tubearig arge e conducted away by a disc througha connection box 19. The location of the tube 17 is indicated by dotted lines.

The cathode filamentis heated by any" convenient-means, such as a battery 20, and

the'main operating current'is supplied bya high potential source of'current, as for example, a transformer;21 connected to the I terminals of the tube by the conductors 22,

23. As shown in Fig. 4, a source of unidi-.

rectional current maybe used when the cathode consists in part of electrically sputtering metal. In this figure an X-ray tube .cury. The tube is operated during the last stages of operation on the pump until the anode is heated to a just visible dull redn'es's' The tube is then sealed off and may be operated without further treatment by a high potential current with the cathode at in-.

candescence.

' Assume the cathode to consist entirely of difiicultly sputtering metal and the anode to consist in part of copper or. other readily sputtering metal and gas to be evolved in some way in the tube and this gas to be ionized by the discharge. .The target 3 in a device operated with alternating current as shown in Fig. 1, when negative in potential will attract the positive ions and some of the copper, silver, gold or the like, will be sputtered, thereby electrically precipitating the ionized gas, and restoring the high vacuum.

When the cathode consists in part of copper, or other electrically sputterable metal, the same effect will be obtained on direct current. Gas ionization will cause positive ions to be attracted to the negative terminal and the impact of the positive ions on the ring 11, or whatever part of the cathode consists of easily sputtered metal, will disintegrate some of the metal and thereby electrically precipitate or fix the gas.

Preferably both the cathode and the anode comprise in part a metal readily sput 'tered in devices intended for operation with alternating current, as the tube is then always ready to respond to incipient positive ionization with electrical vaporization of metal.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A cathode for' an electrical discharge device comprising a conductor adapted to be heated by passage of current, and a member having the same polarity as the cathode and consisting of metal readily sputtered by positive ion bombardment. 2. An electrical discharge device comprising a filament of tungsten adapted to be heated, a member of metal readily sputtered by positive ion bombardment, an anode and an inclosing envelop, the space within said envelop be ng evacuated to a pressure so low that conductlon of electricity may occur substantially independent of positive gas ionization.

3. ,A cathode for an electrical discharge ing electrode, one of said electrodes consisting in part at least of metal readily sputtered by positive ion bombardment, and a source of energy connected to said device having a polarity negative during at least intervals of time with respect to the electrode containing sputterable metal, whereby gas may be electrically precipitated.

6. The process of fixing gas in an exhausted envelop containing a cathode comprising a member adapted tobe heated independently to incandescence, and a coeperating anode, one of said electrodes consisting in part at least of metal readily sputtered electrically, which consists in producing a discharge between said electrodes while the member adapted to be heated is at incandescence, the polarity of the discharge being at least for intervals negative with respect to the electrode containing metal readily sputtered.

7. The process of completing the gas removal in an envelop containing an electrode comprising in part at least metalliccopper, and a cooperating electrode of refractory material adapted to be heated by passage of current, which consists in producing an alternating current discharge between said electrodes while the copper electrode is maintained below the temperature of substantial thermal vaporizatlon, and the cooperating electrode is heated to incandescence. 8. The process of creating and maintainmg ahlgh vacuum in an inclosed rece tacle provided with electrodes, one of which is adapted to be independently heated to incandescence and one of whlch comprises ametal whic h may be electrically sputtered, Wlnch consists in subjecting said receptacle to a preliminary exhaust to a pressure at which a discharge occurs with difficulty from an unheated cathode, then sealing the receptacle, and finally im ressing on thev electrodes while the oath e is heated an alternating current of a potential high enough to sputter metal from the unheated electrode.

' envelop,

. 9. An electrical discharge device comprising a sealed envelop, the space within said envelop being evacuated to a pressure so low that an electron discharge can occur therein independently of gas ionization, a cathode therein adapted to emit electrons independently of gas ionization, and an anode, both of said electrodes consistin in part of metal readily sputtered electrica ly.

10. A thermionic device comprising a sealed envelop, the space within said en- VelOp being evacuated to a pressure so low that a discharge may occur therein independently of gas ionization, a cathode comprising a filament of tungsten and a copper member, and an anode consisting in part at least of copper.

1.1. An X-ray tube comprising a sealed the space within said envelop being evacuated to a pressure so low that an electron discharge may occur therein without substantial gas ionization, a cathode comprising a filament of refractory metal, an anode, a plate of copper extending about said cathode substantially at right angles to an axis passing between cathode and anode.

12. An X-ray .tube comprising the combination of an envelo a cathode of refractory material adapte to be rendered incandescent, an anode, means for fluid-cooling said anode, and plate of copper within said tube connected to have the same polarity as said cathode.

13. An X-ray device comprising the combination of a filamentary cathode consisting of refractory material, means for heating said cathode, an'anode comprising a. copper member, and a discharge-receiving plate of refractory metal, means for circulating a cooling fluid in contact with said anode, a plate of copper electrically connected to said cathode, an inclosing evacuated envelop, and a source of-alternating CUtIJ'I'QIIlJ connected to supply energy to said tu e.. v

14. A "cathode for an X-ray device operating by electron conduction comprising a filament of refractory metal adapted to be rendered incandescent by passage of current, a surrounding tube consisting of refractory metal and a flange of copper connected to and extending substantially at right angles to the tube of refractory metal.

15. A cathode for X-ray devices comprising a flanged tube of refractory metal,- spiral filament of refractory metal located near the mouth of said tube and a ring of metal, such as copper, which is readily sputtered by positive ion bombardment, fastened-to the flange of said tube, and conductors for conveying a heating current to said spiral.

y In witness whereof, I have hereunto set my hand this 2nd day of February 1916.

' WILLIAM D. COOLIDGE. 

